The US Commerce Department is expected to issue soon an opinion on whether auto imports endanger US national security enough to justify import taxes.
US President Donald Trump would then have 90 days to decide whether to impose them, AP reported.
EU spokesman Margaritis Schinas said Monday that if the US goes ahead with "actions detrimental to European exports, the European Commission would react in a swift and adequate manner."
The EU and the US have been trying to work out a trade deal but progress has been slow.